vendredi 1 mai 2009

ADN et groupes humains

Une très vieille humanité.

Dans la revue Science vient d'être publiée une étude scientifique des différentes nations qui peuplent l'Afrique confirmant ce que beaucoup de chercheurs soupçonnaient, les Bushmen ou peuple San, sont le groupe humain le plus ancien sur terre.

L'analyse de son ADN a démontré qu'il se révèlent être le groupe d'humain au patrimoine génétique le plus divers, ce qui est une des caractéristiques de leur proximité avec les humains originaux.

Plus un groupe humain est proche de l'origine commune, plus son patrimoine génétique est riche. En règle générale, plus l'habitat traditionnel d'un groupe est éloigné de l'Afrique, plus son patrimoine génétique est pauvre. Par exemple, les Fuégiens présentent une diversité génétique moins grande que les humains ayant colonisé les approches de l'Afrique.

L'étude de trois mille africains appartenant à 121 populations africaines distinctes (excluant les mulâtres, les métis et populations étrangères) aisni que des groupes haitant en dehors de l'Afrique et a conclu après dix ans de recherches qu'ils descendent tous de 14 populations ancestrales et que l'arbre de leur généalogie génétique est étroitement associée à celui de leurs langues.

Les esprits éclairés, comme Sarah Tishkoff de l'university of Pennsylvanie ont rapidement insisté sur le fait que cette étude prouve que l'Afrique est le « berceau de l'Humanité». Ce qui est une réalité incontestable dans l'état actuel de nos connaissances. Toutefois, rappelons que les Chinois avancent d'autres hypothèses et qu'un jour, peut-être, les faits leur donneront raison.

En revanche, cet usage de l'ADN pour étudier les origines des nations africaines a d'autres conséquences, notamment de valider l'existence de ce que les scientifiques qui ont peur de leur ombre appellent les « groupes continentaux » et qu'aux Etats-Unis on recommence a appeler « races humaines ».

Mais nos lecteurs ont-ils conscience qu'aucun des grands travaux publiés sur la question des races humaines aux Etats-Unis n'a été traduit en France ? Cela en dépit d'un excellent accueil de la communauté scientifique et d'importants succès dans les ventes ?

Signalons que l'UMR 208, IRD-MNHN du musée de l’Homme à Paris a contribué à cette étude. Espérons que cela ne leur vaudra pas d'être ostracisés par leurs collegues humanistes vertueux.

Peintures rupestres attribuées au peuple San.

Evolutionary Genetics:

Africans' Deep Genetic Roots Reveal Their Evolutionary Story

Ann Gibbons

In the largest study ever of African genetic diversity, an international team of researchers has analyzed nuclear DNA collected over a decade from 113 populations of Africans from across the continent. In a report published online in Science this week, the team has found that Africans are descended from 14 ancestral populations, which often correlate with language and cultural groups. They found that all hunter-gatherers and pygmies in Africa today shared ancestors 35,000 years ago and that East Africa was the source of the great migration that populated the rest of the world. They also found that African-American individuals, on average, have mixed ancestry from all over western Africa, which will make it difficult to trace roots to specific ethnic groups.

Voici ce qu'en disent les auteurs

Africa is the source of all modern humans, but characterization of genetic variation and of relationships among populations across the continent has been enigmatic. We studied 121 African populations, 4 African American populations, and 60 non-African populations for patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or linguistic properties. We observe high levels of mixed ancestry in most populations, reflecting historic migration events across the continent. Our data also provide evidence for shared ancestry among geographically diverse hunter-gatherer populations (Khoesan-speakers and Pygmies). The ancestry of African Americans is predominantly from Niger-Kordofanian (~71%), European (~13%), and other African (~8%) populations, although admixture levels varied considerably among individuals. This study helps tease apart the complex evolutionary history of Africans and African Americans, aiding both anthropological and genetic epidemiologic studies.

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